Assortment for the liability to substance abuse is one possible mechanism contributing to its perpetuation in the population. This is due to the fact that assortative mating could elevate the risk for the development of substance abuse in children, relative to randomly mating parents, consequent to increased additive genetic variance of the liability to substance abuse and environmental similarity between parents and children. There is, however, lack of information on homogamy for this liability and on its sources. Particularly, it is not known whether spousal resemblance is caused by phenotypic assortment rather than social homogamy or contagion, and if so, whether it is direct or mediated by assortment for associated personality traits (e.g., aggressiveness, social conventionality, alienation, sensation seeking, etc.). The proposed research has the following specific aims: (1) estimate marital assortment for the liability to substance abuse and associated personality traits; (2) determine the relationship between this liability and associated traits in parents and the behavioral characteristics of their offspring; and, (3) elucidate the effect of primary and secondary marital assortment for the liability to substance abuse and associated characteristics in parents on the behavior characteristics of their offspring. The sample will consist of 200 nuclear families of female and male probands-adult individuals who will be recruited from the community using a reverse telephone book ---complemented with a sample of 200 families of males and females with a diagnosis of substance abuse disorder. The probands will have a son or daughter between 8-11 years of age and a spouse (mate; present or former) accessible for study who is the biological parent of the offspring. Linear structural equation analysis will be applied to test models of primary and secondary assortment. Effects of cohabitation will be tested using hierarchical regression analysis and correlations between spouses' siblings. The hypotheses of phenotypic assortment and social homogamy will be examined using scaling tests. Relationship between parental liability to substance abuse, associated behavioral traits, environmental indices, and behavior in offspring will be investigated. The data obtained will allow for the clarification of the mechanisms influencing variation in the risk for substance abuse. The increased specificity and delineation of factors influencing the liability to substance abuse should facilitate improved detection of high risk children and development of more focused interventions.